This invention relates to a method for use in prevention of plate deformation due to welding thin-gage plates and frames of structures built in rolling stocks, marine vessels, buildings, etc.
In keeping with the recent strong demand for lighter structure in rolling stocks for example, much headway has been made in the use of thin-gage plates for rolling stock structures, more specifically for flat plate welded structures. Aforesaid plates are thin-gage plates of mild steel, stainless steel, aluminum alloy, etc. As thin-gage plates are being widely used, deformation of plates associated with welding is causing problems in view of local stress and appearance of deformed plates.
To solve the problems, as is well known, the three following methods have been used so far:
The first method is shown in FIG. 3. Firstly a plate (a) is welded to a frame (b). Then the plate is locally heated with torch (c) (in the figure, individual points (d) are heated), and further water is applied to the points with hose (e) for quenching. This method is not efficient for its labor required, but also it has a drawback that heated areas are discolored due to the aforementioned local heating, in the case that the plate (a) is of stainless steel.
The second method is represented in Japanese Patent Publication Sho-53-39261. In this method, plates are pulled with strechers while tack-welded to frames. Such welding under pre-tension and successive relief of the tension causes residual tensile stress in the plates, thus resulting in the elimination of the deformation. But this method, on the other hand, depends on an extensive stretching apparatus, resulting in expensive facility cost. Furthermore, in the case that there is an opening in a plate, the opening in a plate prevents the plate from being evenly stretched, thus creating another drawback.
The third method is exemplified in Japanese Patent Publication Sho-53-39262. In this case, with heaters placed close to or in contact with local portions of a plate for heating, the plate is tack welded to a frame while expanded due to heat. Stop of heat supplied from heaters to the plate after welding permits the gradual cooling of the plate, which should lead to deformation due to heat shrinkage. But restriction of the deformation takes place thanks to the frame which has been welded to the plate and causes residual tensile stresses in the plate, thus preventing the plate from being deformed. But this method involves local heating of the plate with heaters, so that it would be impossible to heat uniformly over the whole area of the plate, thus resulting in a poor preventive against plate deformation. On the other hand, it is extremely difficult to exactly control setting temperatures for heating the plate with heaters.